A pedigree shows us the appearance of the certain traits among the direct relatives of the person that we are interested in. Based on a pedigree, we can conclude whether the allele is the dominant or recessive, autosomal or sex-linked.
If the trait is X-linked, males would be predominantly affected. If the trait is expressed by autosomal recessive alleles, the children in the third generation would both be affected. Based on this pedigree chart we can conclude that the widow’s peak hairline is an autosomal dominant trait.

E. dominant allele

D. A chromosome containing the allele for a widow’s peak was passed from parent to offspring in each generation

Right before the start of the meiotic division, genetic material is being doubled. Nondisjunction can occur during meiosis. At the end of a meiotic division, there will be four daughter cells, some of which may be haploid and others aneuploid. When a haploid gamete (YY) merges its genetic material with aneuploid gamete (X) that will result in aneuploidy. The disorder is called the XYY syndrome.

B. Nondisjunction of chromosomes during meiosis

Mendel discovered that alleles for different traits can be dominant or recessive. An exception is the incomplete dominance, where neither one of the two alleles is completely dominant over the other. It means that the heterozygous genotype will not appear as the phenotype of homozygous genotype, recessive nor dominant.

A. If two alleles are codominant then both alleles will be observed in heterozygotes